[v3,5/5] selftests: add fchmodat4(2) selftest
Commit Message
The test marks as skipped if a syscall with the AT_SYMLINK_NOFOLLOW flag
fails. This is because not all filesystems support changing the mode
bits of symlinks properly. These filesystems return an error but change
the mode bits:
newfstatat(4, "regfile", {st_mode=S_IFREG|0640, st_size=0, ...}, AT_SYMLINK_NOFOLLOW) = 0
newfstatat(4, "symlink", {st_mode=S_IFLNK|0777, st_size=7, ...}, AT_SYMLINK_NOFOLLOW) = 0
syscall_0x1c3(0x4, 0x55fa1f244396, 0x180, 0x100, 0x55fa1f24438e, 0x34) = -1 EOPNOTSUPP (Operation not supported)
newfstatat(4, "regfile", {st_mode=S_IFREG|0640, st_size=0, ...}, AT_SYMLINK_NOFOLLOW) = 0
This happens with btrfs and xfs:
$ /kernel/tools/testing/selftests/fchmodat4/fchmodat4_test
TAP version 13
1..1
ok 1 # SKIP fchmodat4(symlink)
# Totals: pass:0 fail:0 xfail:0 xpass:0 skip:1 error:0
$ stat /tmp/ksft-fchmodat4.*/symlink
File: /tmp/ksft-fchmodat4.3NCqlE/symlink -> regfile
Size: 7 Blocks: 0 IO Block: 4096 symbolic link
Device: 7,0 Inode: 133 Links: 1
Access: (0600/lrw-------) Uid: ( 0/ root) Gid: ( 0/ root)
Signed-off-by: Alexey Gladkov <legion@kernel.org>
---
tools/testing/selftests/Makefile | 1 +
tools/testing/selftests/fchmodat4/.gitignore | 2 +
tools/testing/selftests/fchmodat4/Makefile | 6 +
.../selftests/fchmodat4/fchmodat4_test.c | 151 ++++++++++++++++++
4 files changed, 160 insertions(+)
create mode 100644 tools/testing/selftests/fchmodat4/.gitignore
create mode 100644 tools/testing/selftests/fchmodat4/Makefile
create mode 100644 tools/testing/selftests/fchmodat4/fchmodat4_test.c
Comments
* Alexey Gladkov:
> The test marks as skipped if a syscall with the AT_SYMLINK_NOFOLLOW flag
> fails. This is because not all filesystems support changing the mode
> bits of symlinks properly. These filesystems return an error but change
> the mode bits:
>
> newfstatat(4, "regfile", {st_mode=S_IFREG|0640, st_size=0, ...}, AT_SYMLINK_NOFOLLOW) = 0
> newfstatat(4, "symlink", {st_mode=S_IFLNK|0777, st_size=7, ...}, AT_SYMLINK_NOFOLLOW) = 0
> syscall_0x1c3(0x4, 0x55fa1f244396, 0x180, 0x100, 0x55fa1f24438e, 0x34) = -1 EOPNOTSUPP (Operation not supported)
> newfstatat(4, "regfile", {st_mode=S_IFREG|0640, st_size=0, ...}, AT_SYMLINK_NOFOLLOW) = 0
>
> This happens with btrfs and xfs:
>
> $ /kernel/tools/testing/selftests/fchmodat4/fchmodat4_test
> TAP version 13
> 1..1
> ok 1 # SKIP fchmodat4(symlink)
> # Totals: pass:0 fail:0 xfail:0 xpass:0 skip:1 error:0
>
> $ stat /tmp/ksft-fchmodat4.*/symlink
> File: /tmp/ksft-fchmodat4.3NCqlE/symlink -> regfile
> Size: 7 Blocks: 0 IO Block: 4096 symbolic link
> Device: 7,0 Inode: 133 Links: 1
> Access: (0600/lrw-------) Uid: ( 0/ root) Gid: ( 0/ root)
>
> Signed-off-by: Alexey Gladkov <legion@kernel.org>
This looks like a bug in those file systems?
As an extra test, “echo 3 > /proc/sys/vm/drop_caches” sometimes has
strange effects in such cases because the bits are not actually stored
on disk, only in the dentry cache.
Thanks,
Florian
On Tue, Jul 11, 2023 at 02:10:58PM +0200, Florian Weimer wrote:
> * Alexey Gladkov:
>
> > The test marks as skipped if a syscall with the AT_SYMLINK_NOFOLLOW flag
> > fails. This is because not all filesystems support changing the mode
> > bits of symlinks properly. These filesystems return an error but change
> > the mode bits:
> >
> > newfstatat(4, "regfile", {st_mode=S_IFREG|0640, st_size=0, ...}, AT_SYMLINK_NOFOLLOW) = 0
> > newfstatat(4, "symlink", {st_mode=S_IFLNK|0777, st_size=7, ...}, AT_SYMLINK_NOFOLLOW) = 0
> > syscall_0x1c3(0x4, 0x55fa1f244396, 0x180, 0x100, 0x55fa1f24438e, 0x34) = -1 EOPNOTSUPP (Operation not supported)
> > newfstatat(4, "regfile", {st_mode=S_IFREG|0640, st_size=0, ...}, AT_SYMLINK_NOFOLLOW) = 0
> >
> > This happens with btrfs and xfs:
> >
> > $ /kernel/tools/testing/selftests/fchmodat4/fchmodat4_test
> > TAP version 13
> > 1..1
> > ok 1 # SKIP fchmodat4(symlink)
> > # Totals: pass:0 fail:0 xfail:0 xpass:0 skip:1 error:0
> >
> > $ stat /tmp/ksft-fchmodat4.*/symlink
> > File: /tmp/ksft-fchmodat4.3NCqlE/symlink -> regfile
> > Size: 7 Blocks: 0 IO Block: 4096 symbolic link
> > Device: 7,0 Inode: 133 Links: 1
> > Access: (0600/lrw-------) Uid: ( 0/ root) Gid: ( 0/ root)
> >
> > Signed-off-by: Alexey Gladkov <legion@kernel.org>
>
> This looks like a bug in those file systems?
To me this looks like a bug. I'm fine if the operation ends with
EOPNOTSUPP, but in that case the mode bits shouldn't change.
> As an extra test, “echo 3 > /proc/sys/vm/drop_caches” sometimes has
> strange effects in such cases because the bits are not actually stored
> on disk, only in the dentry cache.
tmpfs
syscall_0x1c3(0xffffff9c, 0x7ffd58758574, 0, 0x100, 0x7f6cf18adc70, 0x7ffd58756ad8) = 0
+++ exited with 0 +++
l--------- 1 root root 1 Jul 11 16:36 /tmp/dir/link -> f
=== dropping caches ===
l--------- 1 root root 1 Jul 11 16:36 /tmp/dir/link -> f
ext4
syscall_0x1c3(0xffffff9c, 0x7ffedfdb4574, 0, 0x100, 0x7f7f40b45c70, 0x7ffedfdb3ae8) = -1 EOPNOTSUPP (Operation not supported)
+++ exited with 1 +++
l--------- 1 root root 1 Jul 11 16:36 /tmp/dir/link -> f
=== dropping caches ===
l--------- 1 root root 1 Jul 11 16:36 /tmp/dir/link -> f
xfs
syscall_0x1c3(0xffffff9c, 0x7ffcd03ce574, 0, 0x100, 0x7ff2f2980c70, 0x7ffcd03cdd38) = -1 EOPNOTSUPP (Operation not supported)
+++ exited with 1 +++
l--------- 1 root root 1 Jul 11 16:36 /tmp/dir/link -> f
=== dropping caches ===
l--------- 1 root root 1 Jul 11 16:36 /tmp/dir/link -> f
btrfs
syscall_0x1c3(0xffffff9c, 0x7fff13d2e574, 0, 0x100, 0x7f9b67f59c70, 0x7fff13d2ca88) = -1 EOPNOTSUPP (Operation not supported)
+++ exited with 1 +++
l--------- 1 root root 1 Jul 11 16:36 /tmp/dir/link -> f
=== dropping caches ===
l--------- 1 root root 1 Jul 11 16:36 /tmp/dir/link -> f
reiserfs
syscall_0x1c3(0xffffff9c, 0x7ffdf75af574, 0, 0x100, 0x7f7ad0634c70, 0x7ffdf75ae478) = 0
+++ exited with 0 +++
l--------- 1 root root 1 Jul 11 16:43 /tmp/dir/link -> f
=== dropping caches ===
l--------- 1 root root 1 Jul 11 16:43 /tmp/dir/link -> f
@@ -17,6 +17,7 @@ TARGETS += drivers/net/bonding
TARGETS += drivers/net/team
TARGETS += efivarfs
TARGETS += exec
+TARGETS += fchmodat4
TARGETS += filesystems
TARGETS += filesystems/binderfs
TARGETS += filesystems/epoll
new file mode 100644
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+/*_test
new file mode 100644
@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+CFLAGS += -Wall -O2 -g -fsanitize=address -fsanitize=undefined
+TEST_GEN_PROGS := fchmodat4_test
+
+include ../lib.mk
new file mode 100644
@@ -0,0 +1,151 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#define _GNU_SOURCE
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <syscall.h>
+#include <unistd.h>
+
+#include "../kselftest.h"
+
+#ifndef __NR_fchmodat4
+ #if defined __alpha__
+ #define __NR_fchmodat4 561
+ #elif defined _MIPS_SIM
+ #if _MIPS_SIM == _MIPS_SIM_ABI32 /* o32 */
+ #define __NR_fchmodat4 (451 + 4000)
+ #endif
+ #if _MIPS_SIM == _MIPS_SIM_NABI32 /* n32 */
+ #define __NR_fchmodat4 (451 + 6000)
+ #endif
+ #if _MIPS_SIM == _MIPS_SIM_ABI64 /* n64 */
+ #define __NR_fchmodat4 (451 + 5000)
+ #endif
+ #elif defined __ia64__
+ #define __NR_fchmodat4 (451 + 1024)
+ #else
+ #define __NR_fchmodat4 451
+ #endif
+#endif
+
+int sys_fchmodat4(int dfd, const char *filename, mode_t mode, int flags)
+{
+ int ret = syscall(__NR_fchmodat4, dfd, filename, mode, flags);
+ return ret >= 0 ? ret : -errno;
+}
+
+int setup_testdir(void)
+{
+ int dfd, ret;
+ char dirname[] = "/tmp/ksft-fchmodat4.XXXXXX";
+
+ /* Make the top-level directory. */
+ if (!mkdtemp(dirname))
+ ksft_exit_fail_msg("setup_testdir: failed to create tmpdir\n");
+
+ dfd = open(dirname, O_PATH | O_DIRECTORY);
+ if (dfd < 0)
+ ksft_exit_fail_msg("setup_testdir: failed to open tmpdir\n");
+
+ ret = openat(dfd, "regfile", O_CREAT | O_WRONLY | O_TRUNC, 0644);
+ if (ret < 0)
+ ksft_exit_fail_msg("setup_testdir: failed to create file in tmpdir\n");
+ close(ret);
+
+ ret = symlinkat("regfile", dfd, "symlink");
+ if (ret < 0)
+ ksft_exit_fail_msg("setup_testdir: failed to create symlink in tmpdir\n");
+
+ return dfd;
+}
+
+int expect_mode(int dfd, const char *filename, mode_t expect_mode)
+{
+ struct stat st;
+ int ret = fstatat(dfd, filename, &st, AT_SYMLINK_NOFOLLOW);
+
+ if (ret)
+ ksft_exit_fail_msg("expect_mode: %s: fstatat failed\n", filename);
+
+ return (st.st_mode == expect_mode);
+}
+
+void test_regfile(void)
+{
+ int dfd, ret;
+
+ dfd = setup_testdir();
+
+ ret = sys_fchmodat4(dfd, "regfile", 0640, 0);
+
+ if (ret < 0)
+ ksft_exit_fail_msg("test_regfile: fchmodat4(noflag) failed\n");
+
+ if (!expect_mode(dfd, "regfile", 0100640))
+ ksft_exit_fail_msg("test_regfile: wrong file mode bits after fchmodat4\n");
+
+ ret = sys_fchmodat4(dfd, "regfile", 0600, AT_SYMLINK_NOFOLLOW);
+
+ if (ret < 0)
+ ksft_exit_fail_msg("test_regfile: fchmodat4(AT_SYMLINK_NOFOLLOW) failed\n");
+
+ if (!expect_mode(dfd, "regfile", 0100600))
+ ksft_exit_fail_msg("test_regfile: wrong file mode bits after fchmodat4 with nofollow\n");
+
+ ksft_test_result_pass("fchmodat4(regfile)\n");
+}
+
+void test_symlink(void)
+{
+ int dfd, ret;
+
+ dfd = setup_testdir();
+
+ ret = sys_fchmodat4(dfd, "symlink", 0640, 0);
+
+ if (ret < 0)
+ ksft_exit_fail_msg("test_symlink: fchmodat4(noflag) failed\n");
+
+ if (!expect_mode(dfd, "regfile", 0100640))
+ ksft_exit_fail_msg("test_symlink: wrong file mode bits after fchmodat4\n");
+
+ if (!expect_mode(dfd, "symlink", 0120777))
+ ksft_exit_fail_msg("test_symlink: wrong symlink mode bits after fchmodat4\n");
+
+ ret = sys_fchmodat4(dfd, "symlink", 0600, AT_SYMLINK_NOFOLLOW);
+
+ /*
+ * On certain filesystems (xfs or btrfs), chmod operation fails. So we
+ * first check the symlink target but if the operation fails we mark the
+ * test as skipped.
+ *
+ * https://sourceware.org/legacy-ml/libc-alpha/2020-02/msg00467.html
+ */
+ if (ret == 0 && !expect_mode(dfd, "symlink", 0120600))
+ ksft_exit_fail_msg("test_symlink: wrong symlink mode bits after fchmodat4 with nofollow\n");
+
+ if (!expect_mode(dfd, "regfile", 0100640))
+ ksft_exit_fail_msg("test_symlink: wrong file mode bits after fchmodat4 with nofollow\n");
+
+ if (ret != 0)
+ ksft_test_result_skip("fchmodat4(symlink)\n");
+ else
+ ksft_test_result_pass("fchmodat4(symlink)\n");
+}
+
+#define NUM_TESTS 2
+
+int main(int argc, char **argv)
+{
+ ksft_print_header();
+ ksft_set_plan(NUM_TESTS);
+
+ test_regfile();
+ test_symlink();
+
+ if (ksft_get_fail_cnt() + ksft_get_error_cnt() > 0)
+ ksft_exit_fail();
+ else
+ ksft_exit_pass();
+}